Generally, among hydraulic excavators as construction machines, there are small-sized hydraulic excavators called mini excavators which are suitable for operation in narrow work sites. The upper revolving structure of this small-sized hydraulic excavator is formed to be small so as to be able to revolve even in narrow places.
Here, the small size hydraulic excavator is constituted by an automotive lower traveling structure, an upper revolving structure which is swingably mounted on the lower traveling structure and has a cab provided on a revolving frame constituting a supporting structure, and a working mechanism liftably provided on a front side in the front and rear directions of the upper revolving structure.
The cab of the hydraulic excavator is constituted by a floor member which has on a rear side thereof an operator's seat where an operator is seated and whose front side serves as the operator's footrest area, as well as a cab box which is installed on the floor member and defines an operator's room therein. Further, the cab box is formed by a front side, a rear side, a left side, a right side, and a top side, and an entrance way is provided on the left side for the entrance and exit of the operator to and from the operator's room.
Meanwhile, with the small-sized hydraulic excavator, since the installation space for equipment is limited, the equipment is installed by making use of the space below the floor member. For this reason, in the small-sized hydraulic excavator, the cab is arranged to be supported on the revolving frame so as to be tiltable up and down in a vertical direction by using as a fulcrum the front side position of the floor member so that inspection and maintenance can be provided for the equipment disposed below the floor member (Patent Document 1: Japanese Patent Laid-Open No. 2005-350911 A).
Further, in addition to the operator's seat, control levers, switches, and so on, electrical components and the like for controlling various electrical equipment are provided within the operator's room surrounded by the floor member and the cab box (Patent Document 2: Japanese Patent Laid-Open No. 2005-255109 A).